After reading instructions, complete required steps: In this assignment, implement a binary tree in Python.

Your implementation should have the following methods to the project Week $3-$ Hands On Exercise $-$ Binary Tree Part I:

preorder: This method should return the tree elements in pre$-$order traversal order $($root$,$ left, right$).$

inorder: This method should return the tree elements in in$-$order traversal order $($left$,$ root, right$).$

postorder: This method should return the tree elements in post$-$order traversal order $($left$,$ right, root$).$

Write test cases for each method to ensure that the binary tree is working as expected.